Functional Classification of Neurons
Each part of the nervous system is microscopically characterized by the size, shape, and arrangement of the neurons composing it. Even though some neurons have many internal characteristics in common, their forms vary tremendously. Within that variety, neurons are generally classified according to structure, function, and type of neurotransmitter.
Nerve cells have unique structural properties with important functional consequences; irritability, specific sensitivity, long-distance connectivity, synaptic relations and cohesive integration. The different types of neurons contribute to specific functional properties; long-axon projections cells which are usually excitatory, project long distances and faithfully convey signals with great speed and local circuit interneurons which are usually inhibitory, project nearby and alter transmission in a nucleus, often via an un-myelinated, slowly-conducting axon.
A neuron a cell of ectodermal origin specialized for transmission of information by means of changes in electrical potential across the cell membrane (or any cell autogenetically derived from a clearly neuronal precursor)
a sensory neuron is the first nerve cell on the input side of neuronal processing; typically, directly responsive to stimulation from the external or internal environment. A motor neuron (motoneuron) is the last nerve cell on the output side of neuronal processing: typically, directly innervating muscle cells. An interneuron is any neuron lying between the sensory and motor neurons. (This definition is adhered to quite rigidly by invertebrate neurophysiologist.
Neurons are functionally classified as sensory, motor or interneuron. There are many types of neurons with their own unique structures, like electronic components. Unipolar neurons have one branch/pole. Bipolar neurons have two branches/poles. Multi-polar neurons are neurons with many branches. Projection neurons project to other neurons.
It is not unusual for the cell bodies of neurons to be collected into masses or groups. groups of un-encapsulated neuronal cell bodies in the CNS are called nuclei; in the PNS, such groups, generally encapsulated are called ganglia/ganglion. In the CNS masses of neuronal cell bodies and neuroglia largely contribute to the gray matter of the brain and spinal cord.
Neurons come in a great variety of shapes and patterns subserving many different functions and are classified structurally according to the numbers of their processes. Those without processes or with only one are seen in embryonic neural tissue. Such neurons are termed apolar and unipolar. Neurons with two fused processes that appear as one are called pseudo unipolar and are generally restricted to groups of sensory neuron cell bodies located outside the CNS (ganglia). In these neurons, the short, single process (stem) branching off from the cell body splits into a central process conducting impulses toward the spinal cord and a peripheral process conducting impulses toward the cell body. Impulses moving along the peripheral process probably pass into the cell body before entering the central process. Peripheral and central processes, as well as the stem of the pseudo unipolar neuron, are axonal in structure and function.
Bipolar neurons, are limited to two processes, usually one dendrite and one axon, occasionally two dendrites. Bipolar neurons are found in selected areas such as the ganglia of the VIII cranial nerve, the retina, and the olfactory epithelium. Multipolar neurons are characterized by one axon and two or more dendrites. They are the most common neurons in the nervous system. Golgi I neurons are multipolar cells whose axons extend considerable distances to their target cells. They are found throughout the nervous system, examples here being the pyramidal cell of the cerebral cortex, the Purkinje cell of the cerebellum and the anterior horn cell of the spinal cord. Multipolar neurons with short axons terminating quite close to the cell body of origin are called Golgi II neurons. They are typified by the stellate or granule cells of the cerebral cortex. Of all the neurons, the multipolar seem to exhibit the greatest variety of shapes and sizes.
Sensory neurons conduct impulses from receptors to the brain and spinal cord, such impulses being informational (vision, sound, touch, pain, etc.). Sensory neurons are the sensory (afferent) components of spinal and cranial nerves; their cell bodies largely make up the spinal (posterior root) and cranial ganglia. Sensory neurons are typically pseudo-unipolar or bipolar. Motor neurons conduct impulses from the brain and spinal cord to effectors (muscles and glands) resulting in the contraction of muscle fibers or the secretion of gland cells. Motor neurons are the motor (efferent) component of spinal and cranial nerves. In practice, they are often called lower motor neurons. They are generally multipolar.
However, vertebrate neurophysiologist often use the term interneuron to imply small interneurons whose specific function has not yet been identified, referring to other, better characterized interneurons as, for example, upper motor neurons or second order sensory neurons). Interneurons, a neuron that transmits impulses between other neurons, especially as part of a reflex arc, increase the flexibility of the connections, the bringing together of most of the neurons into a region where they can easily interact: the central nervous system which is protected (in mammals) by a bony framework and the grouping of the processes of the sensory and motor cells into peripheral nerves: the peripheral nervous system.
Interneurons are neurons whose cell bodies and processes remain within the CNS; in other words, they have no direct contact with peripheral structures (receptors and effectors). One important group of interneurons whose axons descend and terminate on motor neurons in the brain stem and spinal cord, are called upper motor neurons. Interneurons are responsible for the modification, coordination, integration, facilitation, and inhibition that must occur between sensory input and motor output. They are the source of the seemingly unlimited array of responses to our environment. interneurons are generally multipolar in structure.
Nerve cells have unique structural properties with important functional consequences; irritability, specific sensitivity, long-distance connectivity, synaptic relations and cohesive integration. The different types of neurons contribute to specific functional properties; long-axon projections cells which are usually excitatory, project long distances and faithfully convey signals with great speed and local circuit interneurons which are usually inhibitory, project nearby and alter transmission in a nucleus, often via an un-myelinated, slowly-conducting axon.
A neuron a cell of ectodermal origin specialized for transmission of information by means of changes in electrical potential across the cell membrane (or any cell autogenetically derived from a clearly neuronal precursor)
a sensory neuron is the first nerve cell on the input side of neuronal processing; typically, directly responsive to stimulation from the external or internal environment. A motor neuron (motoneuron) is the last nerve cell on the output side of neuronal processing: typically, directly innervating muscle cells. An interneuron is any neuron lying between the sensory and motor neurons. (This definition is adhered to quite rigidly by invertebrate neurophysiologist.
Neurons are functionally classified as sensory, motor or interneuron. There are many types of neurons with their own unique structures, like electronic components. Unipolar neurons have one branch/pole. Bipolar neurons have two branches/poles. Multi-polar neurons are neurons with many branches. Projection neurons project to other neurons.
It is not unusual for the cell bodies of neurons to be collected into masses or groups. groups of un-encapsulated neuronal cell bodies in the CNS are called nuclei; in the PNS, such groups, generally encapsulated are called ganglia/ganglion. In the CNS masses of neuronal cell bodies and neuroglia largely contribute to the gray matter of the brain and spinal cord.
Neurons come in a great variety of shapes and patterns subserving many different functions and are classified structurally according to the numbers of their processes. Those without processes or with only one are seen in embryonic neural tissue. Such neurons are termed apolar and unipolar. Neurons with two fused processes that appear as one are called pseudo unipolar and are generally restricted to groups of sensory neuron cell bodies located outside the CNS (ganglia). In these neurons, the short, single process (stem) branching off from the cell body splits into a central process conducting impulses toward the spinal cord and a peripheral process conducting impulses toward the cell body. Impulses moving along the peripheral process probably pass into the cell body before entering the central process. Peripheral and central processes, as well as the stem of the pseudo unipolar neuron, are axonal in structure and function.
Bipolar neurons, are limited to two processes, usually one dendrite and one axon, occasionally two dendrites. Bipolar neurons are found in selected areas such as the ganglia of the VIII cranial nerve, the retina, and the olfactory epithelium. Multipolar neurons are characterized by one axon and two or more dendrites. They are the most common neurons in the nervous system. Golgi I neurons are multipolar cells whose axons extend considerable distances to their target cells. They are found throughout the nervous system, examples here being the pyramidal cell of the cerebral cortex, the Purkinje cell of the cerebellum and the anterior horn cell of the spinal cord. Multipolar neurons with short axons terminating quite close to the cell body of origin are called Golgi II neurons. They are typified by the stellate or granule cells of the cerebral cortex. Of all the neurons, the multipolar seem to exhibit the greatest variety of shapes and sizes.
Sensory neurons conduct impulses from receptors to the brain and spinal cord, such impulses being informational (vision, sound, touch, pain, etc.). Sensory neurons are the sensory (afferent) components of spinal and cranial nerves; their cell bodies largely make up the spinal (posterior root) and cranial ganglia. Sensory neurons are typically pseudo-unipolar or bipolar. Motor neurons conduct impulses from the brain and spinal cord to effectors (muscles and glands) resulting in the contraction of muscle fibers or the secretion of gland cells. Motor neurons are the motor (efferent) component of spinal and cranial nerves. In practice, they are often called lower motor neurons. They are generally multipolar.
However, vertebrate neurophysiologist often use the term interneuron to imply small interneurons whose specific function has not yet been identified, referring to other, better characterized interneurons as, for example, upper motor neurons or second order sensory neurons). Interneurons, a neuron that transmits impulses between other neurons, especially as part of a reflex arc, increase the flexibility of the connections, the bringing together of most of the neurons into a region where they can easily interact: the central nervous system which is protected (in mammals) by a bony framework and the grouping of the processes of the sensory and motor cells into peripheral nerves: the peripheral nervous system.
Interneurons are neurons whose cell bodies and processes remain within the CNS; in other words, they have no direct contact with peripheral structures (receptors and effectors). One important group of interneurons whose axons descend and terminate on motor neurons in the brain stem and spinal cord, are called upper motor neurons. Interneurons are responsible for the modification, coordination, integration, facilitation, and inhibition that must occur between sensory input and motor output. They are the source of the seemingly unlimited array of responses to our environment. interneurons are generally multipolar in structure.